Inversion Of Near-surface Velocities And Quality Factors Based On Rayleigh Wave Dispersion Curve

As a kind of interference wave,surface wave widely exists in seismic records.It has the characteristics of low frequency,low velocity and high amplitude.Most of the traditional studies focus on how to remove the surface wave,but this paper aims to analyze its dispersion property in homogeneous layered media.With the dispersion information,the velocities and quality factors of near surface can be achieved.This technique provides basis for the near-surface statics and amplitude compensation process.The inversion includes three main parts.First is the forward modeling of theoretical model dispersion curves.Second is the extraction of dispersion information,and this paper takes advantage of the simulated seismic data.Third is the inversion process based on the rusults of the second part.This paper implements the fast vector-transfer algorithm and the reflection-transmission coefficient method.Waveform calculation method has been utilized to complement the frequency-wavenumber(f-k)method.By comparing and analyzing the waveform,the dispersion information can be verified,and the mode error can be corrected.Rayleigh wave inversion is a multi-parameter inverse problem.This paper takes p-wave velocity,thickness and density as constant values.Thus the inversion parameters are reduced greatly.In the third part,Levenberg-Marquardt method is adopted,and it bases on the singular value decomposition algorithm.Two kinds of models have been chosen.One is the regular homogeneous layered media,and the other one has a soft layer.This method demonstrated calculation efficiency and stability in the inverse procedure.